In a prior art heat sealing process as shown in U.S. Pat. No. 4,376,005, also known as the EMAWELD process, a thermoplastic matrix loaded with ferromagnetic powder is extruded as a strip and placed between two other plastics surfaces to be fused. The extruded strip is heated by exposing it to a high frequency alternating current and the adjacent plastics surfaces are thus also heated to a temperature at which they fuse with the EMAWELD strip, or with each other. There are disadvantages associated with this method. For example, it is difficult to extrude the plastics when it is loaded with ferromagnetic material, and the whole process is expensive to perform.
It is also known in prior art documents, for example, DE 1,284,618, GB 1,148,044, U.S. Pat. Nos. 5,107,098, 3,047,703 and FR 2,156,472 that a conductive wire can be used in a plastics part so as to fuse the part to a second plastics part by resistance heating. Such a method is used to fuse and seal, e.g. plastics tubes or pipes, motor vehicle fittings, plastics containers or plastics articles.
In certain applications, it would be extremely desirable to be able to seal a plastic strip to another thermoplastics material cheaply and easily. One such application is that of sealing a plastic beading to the hard shell of a suitcase. The plastic beading acts as a water-tight seal to prevent water seeping into the suitcase or as a cushion when the suitcase is closed and the two shells come together. The beading also helps to prevent dust and dirt entering the suitcase.
In more detail, so-called hard side luggage which is typically made of polypropylene or polyethylene often has a plastic beading fitted into grooves around the periphery of the upper and lower shells that make up the suitcase. The plastic beading is made of a soft plastics material, for example, polypropylene, low density polyethylene or ethylvinyl acetate, so that it acts as a cushion. The beading may also be coloured for a pleasing aesthetic effect. Until now, this beading has been attached to the suitcase using adhesives, screws or rivets. This method of fixing is time consuming, labour intensive and therefore expensive. The use of adhesives can give a messy result and screws and rivets tend to look untidy in the finished article. In addition, screws and rivets may cause damage to clothes and can cause injury to the user. They may also become detached from the beading and will then need replacing.
Moulded or hard-side luggage does not usually have an inner lining of cloth or other fabric because there are no frames to conceal the edges of the lining. If a lining is required, a frame will need to be attached for this purpose, with screws or rivets. Again this gives an untidy appearance, and the method of attachment is time-consuming.